<!DOCTYPE html>
<html>
<head>

<style>
	.per{
		width: 100px;
		height: 200px;
		background: #008000;
		position: relative;
		z-index: 5;
	}
	.child{
		width: 50px;
		height: 50px;
		position: relative;
		z-index: 3;
		background: #251500;
	}
</style>
</head>
<body>
	<div class="per">
		<div class="child"></div>
	</div>
</body>
</html>